Q-fever is a systemic infection caused by the intracellular bacterium Coxiella burnetii. The infection is common in animals, especially livestock, and transmitted to humans mainly through the airborne route. The disease presentation varies widely, ranging from asymptomatic infection, acute febrile illness most often with pneumonia, chronic complicated Q-fever (mainly with endocarditis or vascular infection) and post-Q-fever fatigue.
Currently The Netherlands is faced with the most extensive outbreak of Q-fever, related to goat farms. Since 2007, an increasing number of human cases have occurred. The diagnosis is based on a history of exposure, clinical examination and on PCR and serology. Due to the difficulty in culturing Coxiella burnetii in the laboratory, the variation in the antibody response, and the difficulties to standardize serology, the laboratory diagnosis is often not easy. Quite some weight is being given to the phase dependent antibodies, where phase 1 antibodies are seen in chronic infection and the phase 2 antibodies are related to acute infection. With accumulating experience in complicated cases in the current Dutch epidemic, we have experienced that the results of the serology may be equivocal.
If diagnosed in the acute stage, the disease can be cured with a relatively short course of the antibiotic doxycyclin, but chronic Q-fever is a much more difficult-to-treat infection. Chronic Q-fever has a high mortality rate. A special situation is Q-fever in pregnancy, in which the risk for the unborn and the management is not entirely clear.
A special area where the diagnostic tool is critical is the Q-fever vaccination of humans. Currently, patients are screened with serology and a skin test, and only if both tests are negative, vaccination is regarded a safe procedure. The skin test is not easy to perform and laborious. Its sensitivity and specificity are unknown.
There is a need for a specific and sensitive method for diagnosing Q-fever in a subject, circumventing all the drawbacks of existing methods. In addition, the current tests (with the possible exception of the skin test) do not assess the state of specific cellular immunity, which is needed for cure of the infection.